The invention relates to a method in contact-free treatment of a web wherein the web is treated, for example supported, reversed, spread, carried, and/or dried, by means of blowings which provide a carrier-face zone having a curved form. The curved form of the carrier face zone is regulated in a direction transverse to the direction of progress or travel of the web.
The invention also relates to a device in contact-free treatment of a web, in particular in an application of drying, carrying, and/or equivalent of a paper, board or equivalent web. The device comprises a frame part or several frame parts and a nozzle-carrier-face unit arranged in connection with the frame part(s).
As is known in the prior art, in some applications of drying, carrying, etc. of a paper web, board web, or equivalent, a device is needed which is capable of correcting any factors that may be related to the run of the web in the transverse direction of the machine, such as wrinkles, folds, and instabilities of the web. One way to solve these problems is to produce a web curved in the transverse direction of the machine. In contact-free treatment of a web, this can be achieved by creating a curved carrier face for the air nozzles that are used. Airborne web drying is used, e.g., in various coating applications, in particular in applications in which both sides of the web are treated at the same time. One arrangement of this type is the coating-device arrangement marketed by the assignee under the tradename "Sym-Sizer Concept".
With regard to the prior art related to airborne web drying, reference is made to published EP Patent Application Ser. No. 0 507 218 which describes a dryer section including a contact-free web reversing device having a curved form so that the web is turned in the middle of the reversing curve, i.e., corresponding to the middle area of the web, to a greater extent than in lateral areas of the web. Further, in the device, the blow pressures are selected to be higher in the middle area than toward edges areas, so that the web obtains a curved form in the cross direction of the machine. It has been proposed that, by means of this arrangement, formation of waves in the web is reduced in the direction transverse to the running direction of the web, and formation of cockles is avoided. The curved form of the blow pressure profile can be provided either by means of a web reversing device that is accomplished with a curved form or by regulating the blow pressures accordingly. However, in the device described in EP '218, a suitable solution has not been described for carrying out any of the suggested operational modes.
A significant problem related to curved air nozzles is the problem of sealing between the curved and displaceable nozzle and the stationary and straight main frame of the air blow device. Gliding and compressible seals have been used in the prior art apparatus but these seals restrict the possible movement and give rise to associated requirements for servicing and repair thereof, and they often increase the number of various wearing parts.
With further regard to the prior art, reference is made to the EP Patent Application Ser. No. 0 548 419, in which a blow-reversing device is described. This blow-reversing device includes a nozzle part formed in a manner so as to be adjustable, by means of bolts, in a curved position in the cross direction of the machine. This prior art arrangement, however, requires separate and quite complicated sealing arrangements between the nozzle part and the frame part of the device to maintain an adequate seal. Also, in EP '419, in order to regulate the curved form, it is necessary to adjust a number of different screws, and moreover, access to these screws is possible only if other constructional parts of the device are shifted out of the way. Thus, it is a disadvantage of this device that it is difficult to easily and readily regulate its profile to provide the desired curved form.